45% iron base austenitic cr-ni alloy with 18-22% cr, 27-32% ni or (ni+co) plus strengthening additions



June 2, 1964 F T. EBERLE 3,135,602

457, IRON BASE AUSTEINITIC C r-N1. ALLOY WITH 18-22% Cr. 27-52%N/1 OR (NM Co) PLUS STRENGTHENING ADDITIONS Filed Feb. 11, 1957 CREEP-R PT RE STRENGTHS AT 1 P.S.I. X1000 ALLOY 2 ALLOY l H.S.2l

ALLOY 3 CREEPQ-RUPTURE STRENGTHS AT 1800F P.S.l. X 1000 ALLOY 3 ALLOY 2 ALLOY I INVENTOR. Frirz T. Eberle AT TO RNE Y United States Patent O 45% IRON BASE AUSTENITIC Cr-Ni ALLOY WITH 18-22% Cr, 27-32% Ni R (Ni-i-Co) PLUS STRENGTHENING ADDITIONS Fritz T. Eberie, Alliance, Ohio, assignor to The Babcock & Wilcox Company, vNew York, N.Y., a corporation of New Jersey Filed Feb. 11, 1957, Ser. No. 639,520 1 Claim. (Cl. 75-128) This invention relates to precision casting alloys having good long-time high temperature properties and, more particularly, to a precision casting high iron base austenitic alloy relatively lean in scarce or strategic alloying ingredients while having long time high temperature properties equal to or betterthan those of known high Ni and/ or C0 base alloys having such properties.

Where precision cast or shell molded metal parts are intended for longtime service at elevated temperatures of the order of 1600 to- 1800 F., and particularly where it is necessary for such parts to sustain high stresses and resist oxidation during such service, it has hitherto been deemed necessary to form these parts of nickel and/or cobalt base alloys. By the term nickel and/or cobalt base alloys, as used herein, is meantthose alloys in which nickel and/or cobalt comprise in excess of 50% of the alloy constituents, as distinguished from iron or steel alloys in which theiron content is the largest constituent. I I b b 7 Among nickel and/or cobalt base alloys which have been widely used for high stress service at elevated temperatures, particularly in aircraft applications for superchargers, gas turbines and jet engines, are such alloys as HS 21 (62 Co, 2.5 Ni, 27 Cr, 5.5 Mo), HS 25 51 Co, 10. Ni, 20 Cr, 15 w, 1 Fe), 1-1360 70.5 Ni, Cr, 5 Mo, 2 Ch, 6 Al), Hastelloy C (57 Ni, 16 Cr, 17 Mo, 4 W, 5 Fe), and Inconel X (73 Ni, Cr, 0.9 Cb, 2.5 Ti, 0.9 A1, 7 Fe). All of these alloys contain well over 50% of Ni and/ or C0, Whereas the alloys of the present invention contain substantially less than 50% Ni or Ni plus Co.

While nickel and/or cobalt base alloys exemplified by the foregoing have good long time high temperature properties under sustained high stress, their use has been seriously curtailed due to their containing high percentages of scarce or strategic alloying ingredients such as Ni or Co. In addition, such alloying ingredients are sufiiciently expensive, by comparison to the cost of more common elements such as iron, that their use in large quantities is uneconomical. As a result of these factors, considerable research has been carried out in an attempt to develop alloys having properties about equal to those of the nickel and/or cobalt base alloys but containing minimum percentages of scarce, strategic, or expensive elements. Prior to the present invention, however, no satisfactory lean alloys having properties equal to those of the nickel and/or cobalt base alloys have been produced.

In accordance with the present invention, alloys which are lean in strategically scarce materials have been produced which have long time high temperature properties and oxidation resistance, under sustained stresses, equal to or better than the corresponding properties of nickel and/or cobalt base alloys, and which are particularly adaptable to precision casting and shell molding.

More particularly, the present invention is directed to Fe-Cr-Ni alloys containing about 40 to 45% Fe, sufficient chromium to provide oxidation and scaling resistance at temperatures of the order of 2000 F., and sufficient nickel to assure a fully austenitic structure in the presence of up to about 10% of strengthening additions -Paten-ted JuneZ, 1964 selected from the elements Cb, Ta, CbTa, Zr, Mo, W, B, CeLa, and N. The invention is based upon the discovery that, whensuitable amounts and relative concentrations of such strengthening elements, alone or in combination, are added to properly proportioned Fe-Cr-Ni base compositions containing about 40 to 45% Fe, precision cast articles made from the alloys will have rupture strengths at 1600 F. and 1800 F. equal to or better than those of nickel and/ or cobalt base alloys presently used for precision cast articles designed for service under sustained stress at such elevated temperatures.

About 10% to 15% of the Ni may be replaced by Co.

For an understanding of the invention principles, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings. In the drawings, FIGS. 1 and 2 are graphical representations of the comparative creep-rupture strengths ofthe invention alloys at 1600 F. and 1800 F., respectively.

Alloys according to the present invention have the following base composition expressed in percentage by weight: b

Ni (Ni-l-Co) 27.00-32.00 Mn 0.50-2.00

Si 1.25maximum C Balance iron with the usual impurities.

0.40 minimum Alloy (1) Percent Cr 20.00

Ni 27.00 Mn 1.00

CbTa 1.70

W 3.30 Balance iron with the usual impurities.

Alloy (2) Percent Cr 20.00 Ni 15.00

C 0.50 CbTa 2.50

W 2.50 Balance iron with the usual impurities.

Alloy (3) Percent Cr 20.00

Co 12.00 Mn 1.00 Si 0.50 C 0.50 CbTa 2.00 Mo 2.00 W 2.00

Balance iron with the usual impurities.

In each case, the Cb and Ta may be added either as such or as commercial ferro-columbium-tantalum which contains about 41% Cb and 20% Ta.

3 These alloys are distinguished by good castability, high scaling resistance up to 2000 F., and high creep-rupture strength at temperatures up to 1800 F. Examples of the latter obtained on the three preferred compositions given are Stress, p.s.i., for Rupture in Stress, p.s.i., for Rupture 100 hr. 1,000 hr.

6, 800-7, 950 4, 800-5, 700 Alloy (2) 7, 800-8, 400 5, 300-5, 700 Alloy (3) 6, 900 8, 000 5, 0005, 800

Among the better known nickel and/ or cobalt base alloys used for service under sustained stress at elevated temperatures is that known as HS 21 whose composition is 62 Co, 2.5 Ni, 27 Cr, 5.5 Mo. This nickel and cobalt base alloy was selected for comparison purposes in the tests graphically represented in the drawing.

To make a comparison test of the load carrying ability of the invention alloys in comparison with Ni and/or cobalt base alloys, tests were performed on investment cast A" diameter by 1" long specimens with threaded ends in the as-cast condition, that is without any subsequent homogenizing solution treatment and/ or aging treatment. The results of the comparison tests for stress rupture in 100 and 1000 hours at 1600 F. and 1800 F. are shown in the drawing, the left bar graph of each pair being the results in 100 hours and the right bar graph the results in 1000 hours. From these figures, it will be noted that the invention alloys had stress rupture properties substantially equal to that of HS 21.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without depart ing from such principles.

What is claimed is:

An austenitic iron base precision casting alloy having long time hot strength properties at elevated temperatures of the order of 1800 F., and oxidation resistance at elevated temperatures of the order of 2000 F., substantially equivalent to the corresponding properties of nickel base, cobalt base, and nickel-cobalt base alloys containing over of nickel and/or cobalt, said alloy having the following percentage composition by weight:

Cr 20.00 Ni 27.00

CbTa 1.70

Balance from 40.00 to 45.00% iron with the usual impurities.

References Cited in the file of this patent UNITED STATES PATENTS 2,373,490 Mohling Apr. 10, 1945 2,397,034 Mohling Mal. 19, 1946 2,432,615 Franks et al Dec. 16, 1947 2,504,453 Rotherham et a1 Apr. 18, 1950 2,537,477 Mohling et al. Jan. 9, 1951 FOREIGN PATENTS 723,480 France Jan. 18, 1932 2,408,771 Germany Oct. 8, 1946 

